Since the advent of a resist for KrF excimer laser (248 nm), an image forming method called chemical amplification is used as an image forming method for resist so as to compensate for sensitivity reduction caused by light absorption. For example, the image forming method by positive chemical amplification is an image forming method of decomposing an acid generator in the exposed area upon exposure with excimer laser, electron beam, extreme-ultraviolet light or the like to produce an acid, converting an alkali-insoluble group into an alkali-soluble group by using the generated acid as a reaction catalyst in the baking after exposure (PEB: Post Exposure Bake), and removing the exposed area with an alkali developer.
As for the alkali developer used in the method above, various alkali developers have been proposed, but an aqueous alkali developer of 2.38 mass % TMAH (an aqueous tetramethylammonium hydroxide solution) is being used for general purposes.
Also, due to miniaturization of a semiconductor device, the trend is moving toward a shorter wavelength of the exposure light source and a higher numerical aperture (higher NA) of the projection lens, and an exposure machine using an ArF excimer laser with a wavelength of 193 nm as a light source has been developed at present. Furthermore, for example, a so-called immersion method of filling a high refractive-index liquid (hereinafter sometimes referred to as an “immersion liquid”) between the projection lens and the sample, and EUV lithography of performing exposure to ultraviolet light at a shorter wavelength (13.5 nm) have been proposed.
However, it is actually very difficult to find out an appropriate combination of a resist composition, a developer, a rinsing solution and the like, necessary for forming a pattern with overall good performance, and more improvements are being demanded. In particular, as the resolved line width of resist becomes finer, improvement of the line edge roughness performance of a line pattern or the in-plane uniformity of the pattern dimension is being desired.
On the other hand, as well as the currently predominant positive resist, a negative chemical amplification resist composition for use in the pattern formation by alkali development is also being developed (see, for example, JP-A-2006-317803 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2006-259582, JP-A-2006-195050, JP-A-2000-206694). Because, in the production of a semiconductor device or the like, patterns having various profiles such as line, trench and hole need to be formed and some patterns are difficult to form by the current positive resist composition.
In the pattern formation by alkali development using a conventional negative resist composition, it is demanded to more improve the line width variation (LWR), focus latitude (DOF) and other various performances, which are presumed to be mainly governed by swelling at the development.
Also, a double developing technique as a double patterning technology for further raising the resolution is described in JP-A-2008-292975. In this technique, by making use of a property that when exposed, the polarity of a resin in a resist composition becomes high polarity in a high light intensity region and becomes low polarity in a low light intensity region, a high exposure region of a specific resist film is dissolved with a high-polarity developer and a low exposure region is dissolved with a low-polarity developer, whereby the medium exposure dose region is allowed to remain without being dissolved and removed by development and a line-and-space pattern having a pitch half the pitch of the exposure mask is formed.
Furthermore, a chemical amplification resist composition comprising a first resin containing an acid-decomposable repeating unit with a partial structure selected from specific alicyclic hydrocarbon structures and being capable of increasing the polarity by the action of an acid to decrease the solubility for a negative developer (a developer that selectively dissolves and removes the exposed area), and a second resin containing an acid-decomposable repeating unit and being capable of increasing the polarity by the action of an acid to decrease the solubility for a negative developer, with the average content of acid-decomposable repeating units being different from the average content of acid-decomposable repeating units in the first resin, is described in JP-A-2009-025707. It is demonstrated that according to this chemical amplification resist composition, a pattern with little line edge roughness and good performance in terms of pattern collapse is obtained.
However, more stable formation of a high-definition fine pattern for producing a high-precision electronic device with high integration is being demanded.